The present invention relates to press-fit pipe joints, and to methods for making such joints. More specifically, the invention concerns press-fit joints prepared between a length of pipe and another part such as a pipe coupler, where both are composed of a metal which tends to gall under the high pressure conditions existing when making a press fit.
The invention is illustrated herein as it is applied in forming rigid joints between the ends of a length of pipe and couplers connected to such ends to produce a section of pipeline in an irrigation system.
In one form of field irrigation system, multiple sections of pipeline disposed end-to-end are coupled together to produce a continuous expanse of pipe. Wheel structures are provided at intervals along the length of this expanse to support it above the ground, and these are rolled over the ground when repositioning the pipeline in the field being irrigated. In some irrigation systems, power for driving the wheel structures is transmitted through the pipeline itself, and such pipeline in some installations may have considerable length. This means that any joint between a length of pipe and the coupler used to couple the pipe length with an adjacent length of pipe must be capable of reliably transmitting a driving torque of appreciable magnitude. Furthermore, the pressure of the water within the line must be contended with. Obviously, any weakness in a pipe-to-coupler joint will seriously affect the reliability of the irrigation system.
A pipe coupler typically may take the form of a cast aluminum body including a tubular portion at one end which is press fit into the end of a length of pipe to form a joint between them. As is well known, galling occurs when parts composed of certain metals are rubbed against each other under conditions of high pressure, and such metals as aluminum and titanium, and alloys thereof, are especially vulnerable in this regard. Thus, in attempting to press fit a length of aluminum pipe onto a coupler, galling oftentimes will interfere with the obtaining of a proper seated relationship, or will result in the pipe being damaged or severely weakened.
A general object of the present invention, therefore, is to provide an improved press-fit pipe joint which takes care of the above-identified problems in a practical and satisfactory manner.
A more specific object of the invention is to provide means for forming a rigid, press-fit between a length of pipe and a coupler, where the pipe and coupler are of a metal which tends to gall under the conditions existing when making a press fit.
According to a preferred embodiment of the invention, a sheathing element of thin gauge plastic or metal, which exhibits little tendency to gall, is fitted over the end of a length of pipe. The sheathing element includes an inner skirt portion which bounds the inner circumference of the pipe and allows the coupler to be forced into the end of the length of pipe without the galling problems normally experienced.